Mike, does cpuid show sidebanding as enabled?
with my a7n8x del /9800, fastwrites caused instability but sideband addressing worked fine.
It was a pita trying to enable sba with both of my nf2 boards, but I finaly figured out the driver quirk.
fw enabled in mb bios and smartgart = no sba
fw not enabled in mb bios = no sba
fw enabled in bios and disabled in smartgart = sba enabled.
fw's dont usualy provide a noticeable perf gain, but sba does.